Microwave frequency measurement method and device based on microwave photon technology

Abstract

The present invention discloses a microwave frequency measurement method and device based on microwave photonic technology. The method comprises: S1, time-domain stretching the x-polarization state component of an optical frequency comb signal and recombining it with the y-polarization state component; S2, modulating the microwave signal to be measured on the intensity envelope of the recombined optical frequency comb signal; S3, time-domain compressing the x-polarization state component of the modulated optical signal and performing photoelectric conversion, and extracting the pulse time interval of the output electrical signal; separating the y-polarization state component of the modulated optical signal into a measurement signal and a reference signal, introducing a time delay into the measurement signal, performing photoelectric conversion on each of the two resulting electrical signals, and extracting the relative phase of the two resulting electrical signals; S4, calculating the frequency of the microwave signal to be measured based on the pulse time interval and relative phase. The present invention can reduce the requirements for high-speed sampling and strict dispersion matching, and has the advantages of simple structure and high frequency measurement accuracy.

Description

Technical Field

[0001] The present invention relates to a microwave frequency measurement method, in particular to a microwave frequency measurement method based on microwave photon technology. Background Art

[0002] The rapid development of fields such as radar detection, electronic countermeasures, and mobile communications has placed higher demands on real-time, high-precision frequency measurement of broadband microwave signals. This is especially true for fine-grained sensing tasks such as micro-Doppler feature extraction, where frequency measurement accuracy directly determines the ability to perceive the electromagnetic environment and conduct dynamic spectrum management. The micro-Doppler effect, which arises from subtle target motion (such as rotation, vibration, and oscillation), often causes frequency modulation at extremely low frequencies (tens of Hz to kHz). This places extremely high demands on the measurable range and accuracy of frequency measurement systems, making it crucial for accurate target identification and behavioral analysis.

[0003] However, traditional frequency measurement solutions using electrical signal processing face inherent bottlenecks: the front-end is limited by the Nyquist sampling hardware limits of ultra-wide-bandwidth analog-to-digital converters (ADCs), while the back-end faces the challenge of rapidly increasing computational complexity and power consumption of fast Fourier transform (FFT) processing as bandwidth increases. This makes it difficult for measurement systems to strike a balance between bandwidth, speed, dynamic range, and hardware implementation complexity.

[0004] To overcome these electronic bottlenecks, microwave photonics technology offers a new path for building a new generation of high-bandwidth, high-speed frequency measurement systems. By leveraging specific nonlinear effects in the optical domain, the measured frequency can be mapped to specific, easily measurable optical components, thus enabling broadband, real-time frequency measurement of microwave signals. However, the accuracy of these microwave photonic mapping methods is generally difficult to improve. This is because the carrier frequency of optical signals is extremely high (typically on the order of hundreds of terahertz). Minor time or frequency jitter in the system will introduce frequency measurement errors, typically on the order of hundreds of kHz to MHz, making it difficult to measure the Doppler shift of small targets (with a maximum accuracy of tens of Hz). For example, while typical complementary dispersion-based frequency-time mapping frequency measurement methods have some frequency measurement capabilities, they rely on precise matching of dispersion broadening and compression to achieve high accuracy. They also require a high-speed ADC to accurately capture the arrival time of the optical pulses, resulting in complex system architecture and significant integration challenges.

[0005] Therefore, there is an urgent need to develop a microwave photon frequency measurement method and device with simplified structure, fast response, low dispersion matching requirements and easy integration, so as to meet the challenges of real-time and high-precision frequency perception in dynamic spectrum environments, especially for highly sensitive perception tasks such as micro-Doppler frequency shift measurement. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a microwave frequency measurement method based on microwave photonic technology, which can reduce the requirements of traditional photon frequency-time mapping frequency measurement systems for high-speed sampling and strict dispersion matching, and does not require high-speed analog-to-digital conversion, thereby reducing the requirements for digital signal processing. It has the advantages of simple structure and high frequency measurement accuracy.

[0007] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0008] A microwave frequency measurement method based on microwave photon technology comprises the following steps:

[0009] S1, using dispersion value The dispersion element performs time domain broadening on the x-polarization state component of the optical frequency comb signal and then recombines it with the y-polarization state component of the optical frequency comb signal to form a recombined optical frequency comb signal;

[0010] S2. modulating the microwave signal to be measured on the intensity envelope of the recombined optical frequency comb signal to obtain a modulated optical signal;

[0011] S3, using dispersion value The dispersion element performs time domain compression on the x polarization state component of the modulated optical signal and then performs photoelectric conversion, and extracts the pulse time interval of the output electrical signal ; Separate the y polarization state component of the modulated optical signal into a measurement signal and a reference signal containing different comb teeth and introduce a time delay into the measurement signal Then, the reference signal and the measurement signal with time delay are converted into photoelectricity respectively, and the relative phase of the two electrical signals is extracted by phase detection. ;

[0012] S4. Calculate the angular frequency of the microwave signal to be measured according to the following formula: : Where, is the comb tooth angular frequency interval of the optical frequency comb signal, The rounding function.

[0013] Based on the same inventive concept, the following technical solutions can also be obtained:

[0014] A microwave frequency measuring device based on microwave photon technology, comprising:

[0015] Polarization decomposition and time domain broadening modules are used to use the dispersion value The dispersion element performs time domain broadening on the x-polarization state component of the optical frequency comb signal and then recombines it with the y-polarization state component of the optical frequency comb signal to form a recombined optical frequency comb signal;

[0016] an intensity modulation module, configured to modulate the microwave signal to be measured onto the intensity envelope of the recombined optical frequency comb signal to obtain a modulated optical signal;

[0017] Frequency-time mapping and phase detection module is used to use the dispersion value The dispersion element performs time domain compression on the x polarization state component of the modulated optical signal and then performs photoelectric conversion, and extracts the pulse time interval of the output electrical signal ; Separate the y polarization state component of the modulated optical signal into a measurement signal and a reference signal containing different comb teeth and introduce a time delay into the measurement signal Then, the reference signal and the measurement signal with time delay are converted into photoelectricity respectively, and the relative phase of the two electrical signals is extracted by phase detection. ;

[0018] The calculation module is used to solve the angular frequency of the microwave signal to be measured according to the following formula : Where, is the comb tooth angular frequency interval of the optical frequency comb signal, The rounding function.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] Based on the existing frequency-time mapping frequency measurement method based on complementary dispersion, the present invention combines polarization multiplexing and optical frequency comb down-conversion to achieve fast and accurate measurement of microwave frequency, opening up a new direction for microwave photon frequency measurement. The present invention does not require high-speed analog-to-digital conversion, which reduces the requirements for digital signal processing. It can also reduce the requirements of traditional photon frequency-time mapping frequency measurement systems for high-speed sampling and strict dispersion matching, and has the advantages of simple structure and high frequency measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic structural diagram of a microwave frequency measurement device based on microwave photon technology according to the present invention. DETAILED DESCRIPTION

[0022] In view of the shortcomings of the existing frequency-time mapping frequency measurement method based on complementary dispersion, which needs to meet the precise matching of dispersion broadening and compression and high-speed digital sampling, the solution of the present invention is to combine polarization multiplexing and optical frequency comb down-conversion on the basis of the existing frequency-time mapping frequency measurement method based on complementary dispersion to achieve fast and accurate measurement of microwave frequency, thereby reducing the requirements of traditional photonic frequency-time mapping frequency measurement systems for high-speed sampling and strict dispersion matching.

[0023] The microwave frequency measurement method based on microwave photon technology proposed in the present invention comprises the following steps:

[0024] S1, using dispersion value The dispersion element performs time domain broadening on the x-polarization state component of the optical frequency comb signal and then recombines it with the y-polarization state component of the optical frequency comb signal to form a recombined optical frequency comb signal;

[0025] S2. modulating the microwave signal to be measured on the intensity envelope of the recombined optical frequency comb signal to obtain a modulated optical signal;

[0026] S3, using dispersion value The dispersion element performs time domain compression on the x polarization state component of the modulated optical signal and then performs photoelectric conversion, and extracts the pulse time interval of the output electrical signal ; Separate the y polarization state component of the modulated optical signal into a measurement signal and a reference signal containing different comb teeth and introduce a time delay into the measurement signal Then, the reference signal and the measurement signal with time delay are converted into photoelectricity respectively, and the relative phase of the two electrical signals is extracted by phase detection. ;

[0027] S4. Calculate the angular frequency of the microwave signal to be measured according to the following formula: : Where, is the comb tooth angular frequency interval of the optical frequency comb signal, The rounding function.

[0028] The microwave frequency measurement device based on microwave photon technology proposed in the present invention comprises:

[0029] Polarization decomposition and time domain broadening modules are used to use the dispersion value The dispersion element performs time domain broadening on the x-polarization state component of the optical frequency comb signal and then recombines it with the y-polarization state component of the optical frequency comb signal to form a recombined optical frequency comb signal;

[0030] an intensity modulation module, configured to modulate the microwave signal to be measured onto the intensity envelope of the recombined optical frequency comb signal to obtain a modulated optical signal;

[0031] Frequency-time mapping and phase detection module is used to use the dispersion value The dispersion element performs time domain compression on the x polarization state component of the modulated optical signal and then performs photoelectric conversion, and extracts the pulse time interval of the output electrical signal ; Separate the y polarization state component of the modulated optical signal into a measurement signal and a reference signal containing different comb teeth and introduce a time delay into the measurement signal Then, the reference signal and the measurement signal with time delay are converted into photoelectricity respectively, and the relative phase of the two electrical signals is extracted by phase detection. ;

[0032] The calculation module is used to solve the angular frequency of the microwave signal to be measured according to the following formula : Where, is the comb tooth angular frequency interval of the optical frequency comb signal, The rounding function.

[0033] In order to facilitate public understanding, the technical solution of the present invention is described in detail below with reference to the accompanying drawings:

[0034] The basic structure of the microwave frequency measuring device of the present invention is as follows: Figure 1 As shown, it includes two dispersion elements, a polarization controller, two polarization beam splitters, a polarization beam combiner, a wavelength division multiplexer, an intensity modulator, three photodetectors and a solution module (not shown in the figure).

[0035] like Figure 1 As shown, a polarization controller and a polarization beam splitter are first used to decompose the optical frequency comb signal into mutually orthogonal x-polarization state components and y-polarization state components. In the x-polarization state branch, the optical signal is time-domain stretched by a dispersion element 1 and then input to a polarization beam combiner. In the y-polarization state branch, the optical signal is directly input to the polarization beam combiner. The two signals are recombined and output in the polarization beam combiner to produce a recombined optical frequency comb signal.

[0036] Subsequently, the microwave signal to be measured is modulated on the intensity envelope of the recombined optical frequency comb signal by an intensity modulator;

[0037] The modulated optical signal obtained is further divided into two paths, the x polarization state and the y polarization state, after passing through the polarization beam splitter 2: in the x polarization state branch, the optical signal is compressed in the time domain by the dispersion element 2, and the dispersion element 2 has the opposite dispersion amount to the dispersion element 1, thereby realizing the frequency-time mapping of the microwave signal to be measured, and then performing photoelectric detection; in the y polarization state branch, the optical signal is first separated into a measurement signal and a reference signal containing different comb teeth by a wavelength division multiplexer, and then a fixed delay is introduced into the measurement signal through an optical delay line, so that the two signals have a certain time difference when they reach the photoelectric detector; after the two signals are respectively converted into photoelectricity, the electrical signals corresponding to the measurement signal and the reference signal are output; finally, the system obtains a total of three sets of electrical signals, which come from: the x polarization state branch; the measurement channel in the y polarization state branch; and the reference channel in the y polarization state branch;

[0038] The above-mentioned electrical signals are sampled and processed using a low-speed ADC. In the output signal of the x-polarization state branch, the frequency information of the microwave signal to be measured is mapped to the pulse time interval of the output electrical signal, and this pulse time interval is extracted. In the output photocurrent signal of the y-polarization state branch, the phase of the electrical signal of the measurement channel relative to the electrical signal of the reference channel is extracted through phase detection. Finally, by combining the pulse time interval of the x-polarization state branch with the phase information of the y-polarization channel, the frequency of the microwave signal to be measured can be quickly and accurately determined.

[0039] The principle of the technical solution of the present invention is further described in detail below:

[0040] The input optical frequency comb signal can be expressed as:

[0041]

[0042] in, The optical frequency comb Root comb teeth, For the The complex envelope amplitude of the optical frequency comb teeth, is the angular frequency of the center frequency component of the optical frequency comb, is the angular frequency interval of the optical frequency comb teeth.

[0043] After passing through the polarization controller and polarization beam splitter 1, the input signal is decomposed into orthogonal ground states:

[0044]

[0045] in, .

[0046] The group velocity dispersion is introduced into the x-polarization state branch through the dispersion element 1, and its dispersion value is ,in, is the second-order propagation coefficient of electromagnetic waves in dispersive media (i.e., group velocity dispersion), is the length of dispersion element 1. Then the frequency response of dispersion element 1 is:

[0047]

[0048] After the x-polarization state branch signal undergoes time domain stretching, the two signals are recombined in the polarization beam combiner. The recombined signal is:

[0049]

[0050] in, for The Fourier transform of , that is, the time domain impulse response corresponding to dispersion element 1.

[0051] The recombined optical signal enters the electro-optical intensity modulator, which modulates the microwave signal to be measured onto the recombined optical frequency comb signal in the form of intensity modulation. Assume that the microwave signal to be measured is In the case of small signal modulation, the modulated signal can be expressed as:

[0052]

[0053] in, A is the modulation index of intensity modulation.

[0054] The optical signal of the x-polarization state branch then undergoes time domain compression through the dispersion element 2, and the output signal is:

[0055]

[0056] in, for The Fourier transform of the time domain impulse response of dispersion element 2 is the Fourier transform of dispersion element 1. When dispersion element 1 and dispersion element 2 have opposite dispersion values, the frequency-time mapping of the microwave signal to be measured can be realized. For convenience, it is assumed that the microwave signal to be measured is expressed as , To measure microwave signals The angular frequency of , then Equation (6) can be simplified to:

[0057]

[0058] From formula (7), we can see that in the time domain, , There is a pulse signal at each moment. The optical signal is input into the low-speed photoelectric detector for photoelectric conversion. By collecting and extracting the time interval between pulses, the angular frequency measurement value with error of the microwave signal to be measured can be obtained. :

[0059]

[0060] in, is the time interval between pulses. In the x-polarization state branch, the frequency information of the microwave signal to be measured is mapped to the time interval of the output electrical pulses.

[0061] The y polarization state branch is separated into the measurement signal and the reference signal by a wavelength division multiplexer, and a time delay is introduced into the measurement channel. The output signal after is:

[0062]

[0063] The optical signal is input into the low-speed photodetector for photoelectric conversion. When , the microwave signal to be measured realizes optical down-conversion after photoelectric conversion. At this time, the photocurrent signal output by the measurement channel can be expressed as:

[0064]

[0065] in, is the electro-optical conversion coefficient of the photodetector; K is a non-negative integer that satisfies , The rounding function.

[0066] Since the reference signal of the y-polarization state branch has no fixed time delay relative to the measurement channel, the obtained electrical signal has a phase difference (i.e., relative phase) compared to the reference signal. Through phase detection, the relative phase of the measurement channel photocurrent relative to the reference channel photocurrent can be measured as:

[0067]

[0068] in, .

[0069] In summary, the joint 、 , formula (8), formula (11), we get:

[0070]

[0071] Solving the above equations can determine the exact angular frequency of the microwave signal to be measured. .

[0072] Obviously, the roles of the x polarization state and the y polarization state in the above measurement process are interchangeable.

[0073] Assume that the phase detection accuracy is , it can be seen that the frequency measurement accuracy of the frequency measurement scheme of the present invention is for:

[0074]

[0075] Where, Introducing delay control error into the optical delay line.

[0076] In summary, the present invention, based on the existing frequency-time mapping frequency measurement method based on complementary dispersion, combines optical polarization division multiplexing and optical frequency comb down-conversion, which can reduce the requirements of traditional photonic frequency-time mapping frequency measurement systems for high-speed sampling and strict dispersion matching, and does not require high-speed analog-to-digital conversion, thereby reducing the requirements for digital signal processing. It has the advantages of simple structure, high frequency measurement accuracy and easy integration. It is suitable for real-time spectrum sensing needs in dynamic electromagnetic environments, and is particularly suitable for small frequency shift measurement scenarios such as micro-Doppler.

Claims

1. A microwave frequency measurement method based on microwave photon technology, characterized in that: The following steps are involved: S1, using dispersion value After the dispersion element performs time domain stretching on the x polarization state component of the optical frequency comb signal, the x polarization state component of the time domain stretched optical frequency comb signal is recombined with the y polarization state component of the optical frequency comb signal to form a recombined optical frequency comb signal; S2. modulating the microwave signal to be measured on the intensity envelope of the recombined optical frequency comb signal to obtain a modulated optical signal; S3, using dispersion value The dispersion element performs time domain compression on the x polarization state component of the modulated optical signal and then performs photoelectric conversion, and extracts the pulse time interval of the output electrical signal ; Separate the y polarization state component of the modulated optical signal into a measurement signal and a reference signal containing different comb teeth and introduce a time delay into the measurement signal Then, the reference signal and the measurement signal with time delay are converted into photoelectricity respectively, and the relative phase of the two electrical signals is extracted by phase detection. ; S4. Calculate the angular frequency of the microwave signal to be measured according to the following formula: : Where, is the comb tooth angular frequency interval of the optical frequency comb signal, The rounding function.

2. A microwave frequency measurement device based on microwave photon technology, characterized in that: include: Polarization decomposition and time domain broadening modules are used to use the dispersion value After the dispersion element performs time domain stretching on the x polarization state component of the optical frequency comb signal, the x polarization state component of the time domain stretched optical frequency comb signal is recombined with the y polarization state component of the optical frequency comb signal to form a recombined optical frequency comb signal; an intensity modulation module, configured to modulate the microwave signal to be measured onto the intensity envelope of the recombined optical frequency comb signal to obtain a modulated optical signal; Frequency-time mapping and phase detection module is used to use the dispersion value The dispersion element performs time domain compression on the x polarization state component of the modulated optical signal and then performs photoelectric conversion, and extracts the pulse time interval of the output electrical signal ; Separate the y polarization state component of the modulated optical signal into a measurement signal and a reference signal containing different comb teeth and introduce a time delay into the measurement signal Then, the reference signal and the measurement signal with time delay are converted into photoelectricity respectively, and the relative phase of the two electrical signals is extracted by phase detection. ; The calculation module is used to solve the angular frequency of the microwave signal to be measured according to the following formula : Where, is the comb tooth angular frequency interval of the optical frequency comb signal, The rounding function.

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