Frequency measurement method and device based on microwave photon frequency-time mapping

Abstract

The invention discloses a frequency measurement method based on microwave photon frequency-time mapping, and the method comprises the steps: firstly carrying out the microwave photon frequency multiplication processing of a to-be-measured microwave signal, obtaining an N-frequency multiplication signal of the to-be-measured microwave signal, and N is an integer greater than or equal to 2; and then measuring frequency and amplitude information of the N-frequency multiplication signal by using a microwave photon frequency-time mapping method based on real-time Fourier transform, and further obtaining frequency and amplitude information of a microwave signal to be measured with the resolution improved to N times. The invention also discloses a frequency measurement device based on microwave photon frequency-time mapping. On the basis of an existing microwave photon frequency-time mapping method based on real-time Fourier transform, microwave photon frequency multiplication processing is carried out on a microwave signal to be detected, and as pulse interval time in a time domain waveform is stretched and amplified in an equal ratio, the problem of signal aliasing caused by too small time interval is avoided; therefore, the frequency measurement resolution is effectively improved.

Description

Technical Field

[0001] The present invention relates to a frequency measurement method, and more particularly to a frequency measurement method based on microwave photon frequency-time mapping. Background Art

[0002] Microwave signals generally refer to electromagnetic wave signals with a frequency range from 300 MHz to 300 GHz (corresponding to a wavelength from 1 m to 1 mm), which can be mathematically expressed as where A is the amplitude of the microwave signal, ω and are the frequency and initial phase respectively. Since microwave signals in different frequency bands have their own performance characteristics, microwave signals have been widely used in various aspects of military life, such as electronic warfare, radar, wireless communication, autonomous driving, aerospace, navigation, medical treatment, and geological exploration. The electronics method is a traditional means to realize microwave frequency measurement. According to its different structures, it can be divided into fixed-frequency frequency measurement method, multi-channel frequency measurement method, superheterodyne frequency measurement method, multi-channel superheterodyne frequency measurement method, instantaneous frequency measurement method, pulse compression frequency measurement method, digital frequency measurement method, etc. Table 1 summarizes the characteristics of the above several electrical microwave frequency measurement methods. It can be seen that different microwave frequency measurement methods have different advantages and disadvantages. The traditional electronics frequency measurement method has a small working bandwidth, and it is difficult to balance frequency resolution and frequency real-time performance, and it is not suitable for broadband, real-time, and high-resolution frequency measurement in a complex electronic spectrum environment.

[0003]

[0004] Table 1: Performance Comparison of Electrical Microwave Frequency Measurement Methods

[0005] In view of the above key problems of the electronics frequency measurement method, the development of photon technology provides an effective solution. In the measurement based on photon technology, researchers at home and abroad have carried out a lot of research. According to different measurement principles, microwave frequency measurement based on microwave photon technology can be divided into: frequency-power mapping method, frequency-space mapping method, frequency-time mapping method, spatial spectrum material method, and compressive sensing method. Table 2 gives the comparison of the advantages and disadvantages of the above photonics microwave frequency measurement methods.

[0006]

[0007] Table 2: Advantages and Disadvantages of Photonics Microwave Frequency Measurement Methods

[0008] In the above microwave frequency measurement technology based on microwave photon technology, the frequency-time mapping (hereinafter referred to as frequency-time mapping) technology based on real-time Fourier transform uses positive and negative dispersion media to achieve spectrum analysis through optical-domain frequency-time mapping, transfers the processing process to the analog optical domain, breaks through the operation bottleneck of traditional digital Fourier transform, and can complete real-time processing of high-frequency signals without complex algorithms; directly analyzes frequency-domain information through time-domain waveforms, significantly reduces the data volume and improves the processing speed; in addition, its system architecture is simple, and the single-link design has the ability to process multi-frequency signals, avoiding the dependence on complex devices such as optical frequency combs. However, this scheme calculates frequency information using the time-domain waveform after frequency-time mapping. There is a linear relationship between the time interval between the reference pulse and the signal pulse in the time-domain waveform and the frequency of the microwave signal to be measured. When the frequency of the microwave signal to be measured is low, aliased signals that cannot be recognized due to too small time intervals will affect the resolution of frequency measurement. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to overcome the problem of low frequency measurement resolution existing in the existing microwave photon frequency-time mapping method based on real-time Fourier transform, and provide a frequency measurement method based on microwave photon frequency-time mapping, which can effectively improve the frequency measurement resolution of the microwave photon frequency-time mapping method based on real-time Fourier transform.

[0010] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0011] A frequency measurement method based on microwave photon frequency-time mapping. First, perform microwave photon frequency doubling processing on the microwave signal to be measured to obtain an N-fold frequency signal of the microwave signal to be measured, where N is an integer greater than or equal to 2; then use the microwave photon frequency-time mapping method based on real-time Fourier transform to measure the frequency and amplitude information of the N-fold frequency signal, and further obtain the frequency and amplitude information of the microwave signal to be measured with the resolution improved to N times.

[0012] Preferably, the method of microwave photon frequency doubling processing is specifically as follows: through a dual-parallel Mach-Zehnder modulator operating at the maximum transmission point, modulate the microwave signal to be measured on a continuous optical carrier to generate a modulated optical signal that only contains positive and negative second-order optical sidebands and the optical carrier; filter out the optical carrier in the modulated optical signal; perform photoelectric detection on the modulated optical signal after filtering out the optical carrier to obtain a 4-fold frequency signal of the microwave signal to be measured.

[0013] Further preferably, a micro-ring filter is used to filter out the optical carrier in the modulated optical signal.

[0014] Based on the same inventive concept, the following technical solutions can also be obtained:

[0015] A frequency measurement device based on microwave photon frequency-time mapping, comprising:

[0016] A frequency multiplication module, which is used to perform microwave photonic frequency multiplication processing on the microwave signal to be measured, and obtain an N-fold frequency signal of the microwave signal to be measured, where N is an integer greater than or equal to 2;

[0017] A microwave photonic frequency-time mapping frequency measurement module, which is used to measure the frequency and amplitude information of the N-fold frequency signal by using the microwave photonic frequency-time mapping method based on real-time Fourier transform, and then obtain the frequency and amplitude information of the microwave signal to be measured with the resolution improved to N times.

[0018] Preferably, the frequency multiplication module includes:

[0019] A dual-parallel Mach-Zehnder modulator, which operates at the maximum transmission point and is used to modulate the microwave signal to be measured on a continuous optical carrier to generate a modulated optical signal that only contains positive and negative second-order optical sidebands and the optical carrier;

[0020] An optical filter, which is used to filter out the optical carrier in the modulated optical signal;

[0021] A photodetector, which is used to perform photoelectric detection on the modulated optical signal after filtering out the optical carrier to obtain a 4-fold frequency signal of the microwave signal to be measured.

[0022] More preferably, the optical filter is a micro-ring filter.

[0023] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0024] Based on the existing microwave photonic frequency-time mapping method based on real-time Fourier transform, the present invention performs microwave photonic frequency multiplication processing on the microwave signal to be measured to obtain a frequency multiplication signal of the microwave signal to be measured, and then uses the microwave photonic frequency-time mapping method based on real-time Fourier transform to measure the frequency and amplitude information of the frequency multiplication signal, and then obtains the frequency and amplitude information of the microwave signal to be measured according to the frequency multiplication factor; since the pulse interval time in the time-domain waveform is stretched and amplified in equal proportion, the signal aliasing problem caused by too small time interval is avoided, thereby effectively improving the frequency measurement resolution. Description of the Drawings

[0025] Figure 1 It is a structural block diagram of a specific embodiment of the frequency measurement device based on microwave photonic frequency-time mapping of the present invention;

[0026] Figure 2 It is a specific implementation structure of the frequency multiplication module. Detailed Embodiments

[0027] Aiming at the problem of low frequency measurement resolution existing in the existing microwave photon frequency-time mapping method based on real-time Fourier transform, the solution idea of the present invention is to add a frequency doubling module on this basis. First, perform microwave photon frequency doubling processing on the microwave signal to be measured to obtain the frequency-doubled signal of the microwave signal to be measured, and then use the microwave photon frequency-time mapping method based on real-time Fourier transform to measure the frequency and amplitude information of the frequency-doubled signal, and then obtain the frequency and amplitude information of the microwave signal to be measured according to the frequency doubling multiple; since the pulse interval time in the time domain waveform is stretched and amplified in a geometric ratio, the signal aliasing problem caused by too small time interval is avoided, thereby effectively improving the frequency measurement resolution.

[0028] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0029] A frequency measurement method based on microwave photon frequency-time mapping. First, perform microwave photon frequency doubling processing on the microwave signal to be measured to obtain the N-fold frequency-doubled signal of the microwave signal to be measured, where N is an integer greater than or equal to 2; then use the microwave photon frequency-time mapping method based on real-time Fourier transform to measure the frequency and amplitude information of the N-fold frequency-doubled signal, and then obtain the frequency and amplitude information of the microwave signal to be measured with the resolution improved to N times.

[0030] A frequency measurement device based on microwave photon frequency-time mapping, comprising:

[0031] A frequency doubling module for performing microwave photon frequency doubling processing on the microwave signal to be measured to obtain the N-fold frequency-doubled signal of the microwave signal to be measured, where N is an integer greater than or equal to 2;

[0032] A microwave photon frequency-time mapping frequency measurement module for using the microwave photon frequency-time mapping method based on real-time Fourier transform to measure the frequency and amplitude information of the N-fold frequency-doubled signal, and then obtaining the frequency and amplitude information of the microwave signal to be measured with the resolution improved to N times.

[0033] For the convenience of public understanding, the technical solutions of the present invention will be described in detail below through a specific embodiment in conjunction with the drawings:

[0034] The basic structure of the frequency measurement device in this embodiment is as Figure 1 shown, including: a light source, an optical filter, a positive chirped fiber grating, an optical amplifier, an intensity modulator, a bias point control module, an optical splitter, a negative chirped fiber grating, a photodetector, a main control module, etc.

[0035] Among them, the light source is a femtosecond laser, which is used to generate femtosecond-level ultra-narrow optical pulse signals; the positive chirped fiber grating has large dispersion and is used to stretch the time-domain ultra-narrow optical pulse to an appropriate time window, facilitating subsequent modulation of the microwave signal to be measured onto the optical pulse signal; the intensity modulator is used to modulate the microwave signal to be measured onto the optical pulse for real-time spectrum analysis; the negative chirped fiber grating has a dispersion amount opposite to that of the positive chirped fiber grating and is used to compress the time-domain pulse and map the signal spectrum onto the time-domain waveform; the bias point control module is used to control the bias voltage of the intensity modulator to make it work stably at the minimum transmission operating point to generate a carrier-suppressed optical double-sideband signal; the optical amplifier is used to compensate for the loss of the optical signal during transmission in the link; the photodetector is used to convert the optical signal into an electrical signal for subsequent sampling and processing of the signal by a data acquisition device; the main control module is used for program control of the devices inside the chassis on the one hand, and on the other hand, processes and displays the real-time spectrum analysis data obtained by sampling through the developed software.

[0036] The part except the frequency doubling module is an existing frequency measurement device based on microwave photon frequency-time mapping. The improvement of the present invention lies in adding a frequency doubling module. First, the microwave photon frequency doubling process is performed on the microwave signal to be measured by the frequency doubling module to obtain the N-fold frequency signal of the microwave signal to be measured, where N is an integer greater than or equal to 2; then the N-fold frequency signal is input into the existing frequency measurement device based on microwave photon frequency-time mapping, and the frequency amplitude information of the N-fold frequency signal can be obtained. Since the frequency doubling multiple N is known, it is easy to obtain the frequency amplitude information of the microwave signal to be measured.

[0037] The frequency doubling module can adopt various existing microwave photon frequency doubling schemes. In this embodiment, a microwave photon frequency doubling device based on a dual parallel Mach-Zehnder modulator (DPMZM) is adopted, and its structure is as Figure 2 shown, including a laser, a DPMZM, a microring filter, and a photodetector.

[0038] The microwave signal to be measured (taking the linear frequency modulation signal LFM as an example) is modulated onto the continuous optical carrier emitted by the laser through the DPMZM; the DPMZM is made to work at the maximum transmission point to suppress the odd-order optical sidebands and output the even-order optical sidebands and the optical carrier. The amplitude of the radio frequency signal is adjusted so that the output optical signal of the DPMZM only contains the positive and negative second-order optical sidebands and the optical carrier, and the power of the higher-order sidebands is small and can be ignored; then the modulated optical signal output by the DPMZM can be expressed as:

[0039] E DPMRR (t) = J0(m)cos(2πf c t) + J2(m)cos[2π(f c + 2f LFM )

[0040] + J2(m)cos[2π(fc -2f LFM )t]

[0041] where: m is the modulation index; J0 and J2 are the zero-order and second-order Bessel functions of the first kind, respectively.

[0042] In this embodiment, a microring resonator filter is used for filtering. The microring resonator filter is an optical filter based on the microring resonator structure, which has the advantages of high integration and tunability. By using the microring resonator filter to filter out the optical carrier component in the modulated optical signal, leaving the positive and negative second-order optical sidebands to enter the photodetector (PD) for photoelectric conversion, a four-fold frequency LFM signal can be obtained.

[0043] The four-fold frequency LFM signal is input into the existing frequency measurement device based on microwave photon frequency-time mapping. The time-domain output waveforms corresponding to different frequencies of the RF signal to be measured are quadrupled in frequency, and the time interval is stretched four times at the same time, avoiding the signal aliasing problem caused by too small time interval, thus effectively improving the frequency measurement resolution.

Claims

1. A frequency measurement method based on microwave photon frequency-time mapping, characterized in that: First, microwave photon frequency doubling processing is performed on the microwave signal to be measured to obtain an N-fold frequency signal of the microwave signal to be measured, where N is an integer greater than or equal to 2; then a microwave photon frequency-time mapping method based on real-time Fourier transform is used to measure the frequency and amplitude information of the N-fold frequency signal, thereby obtaining the frequency and amplitude information of the microwave signal to be measured with a resolution improved to N times.

2. The frequency measurement method based on microwave photon frequency-time mapping as claimed in claim 1, characterized in that: The method for microwave photon frequency doubling processing is specifically as follows: a microwave signal to be measured is modulated on a continuous optical carrier by a dual parallel Mach-Zehnder modulator working at a maximum transmission point to generate a modulated optical signal containing only positive and negative second-order optical sidebands and an optical carrier; the optical carrier in the modulated optical signal is filtered out; and the modulated optical signal after filtering out the optical carrier is photoelectrically detected to obtain a 4-fold frequency signal of the microwave signal to be measured.

3. The frequency measurement method based on microwave photon frequency-time mapping as claimed in claim 2, characterized in that: A micro-ring filter is used to filter out the optical carrier in the modulated optical signal.

4. A frequency measurement device based on microwave photon frequency-time mapping, characterized in that: include: A frequency doubling module, used for performing microwave photon frequency doubling processing on the microwave signal to be measured, to obtain an N-fold frequency signal of the microwave signal to be measured, where N is an integer greater than or equal to 2; The microwave photon frequency-time mapping frequency measurement module is used to measure the frequency and amplitude information of the N-fold frequency signal using a microwave photon frequency-time mapping method based on real-time Fourier transform, thereby obtaining the frequency and amplitude information of the microwave signal to be measured with a resolution increased to N times.

5. The frequency measuring device based on microwave photon frequency-time mapping as claimed in claim 4, characterized in that: The frequency multiplication module comprises: A dual parallel Mach-Zehnder modulator, which operates at a maximum transmission point, is used to modulate the microwave signal to be measured on a continuous optical carrier to generate a modulated optical signal containing only positive and negative second-order optical sidebands and the optical carrier; An optical filter, used for filtering out an optical carrier in the modulated optical signal; The photoelectric detector is used to perform photoelectric detection on the modulated optical signal after filtering out the optical carrier, and obtain a 4-fold frequency signal of the microwave signal to be measured.

6. The frequency measuring device based on microwave photon frequency-time mapping as claimed in claim 5, characterized in that: The optical filter is a micro-ring filter.

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