Instantaneous microwave frequency measurement method and system based on double electro-optic comb vernier measurement method

Abstract

The application discloses a kind of instantaneous microwave frequency measurement method and system based on double electro-optical comb vernier measurement method, laser emitted by light source is used for intensity modulation with detection microwave respectively, local light comb with small repetition frequency difference is generated, and after detection light comb, the signal after intensity modulation is respectively frequency modulated with local light comb after radio frequency and radio frequency after detection light comb, based on vernier effect, the position of comb tooth close to the frequency of microwave to be measured is determined according to the difference of the difference of two frequency differences, and microwave frequency is accurately positioned in the left, right or middle of local light comb and detection light comb comb tooth position, and then microwave signal frequency is obtained.The application has wide frequency coverage, large instantaneous bandwidth, high measurement accuracy, fast measurement speed, and can realize simultaneous measurement of multiple microwave frequencies, with low system complexity and low system cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microwave measurement, and particularly relates to a method and system for measuring instantaneous microwave frequency based on a double electro-optical comb vernier measurement method. BACKGROUND

[0002] Existing instantaneous microwave frequency measurement generally uses a pure electrical method, but such a technology is not only extremely complex and expensive, but also limited by the bandwidth of electronic devices, and it is difficult to realize instantaneous frequency measurement above 10GHz. The existing microwave instantaneous frequency measurement technology based on optical frequency comb modulates the phase of the optical comb teeth, and then performs Brillouin frequency shift in a high nonlinear optical fiber. The frequency nonlinear characteristics of the Brillouin frequency shift make the frequency shift amount of the sideband signal loaded on each comb tooth different. A monotonic correlation between the frequency of the signal to be measured and the power of the photodetector is established between each two channels, and the frequency value of the signal to be measured is obtained by reading the power value of the photodetector. However, the frequency measurement accuracy of this kind of technology is difficult to determine, and the error in the actual measurement reference process is large. SUMMARY

[0003] The present application proposes a method and system for measuring instantaneous microwave frequency based on a double electro-optical comb vernier measurement method, which has a wide measurement frequency coverage, a large instantaneous bandwidth, a high measurement accuracy, a fast measurement speed, and can realize simultaneous measurement of multiple microwave frequencies, has low system complexity and low system cost.

[0004] The present application is achieved by the following technical solutions:

[0005] The present application relates to a method for measuring instantaneous microwave frequency based on a double electro-optical comb vernier measurement method. The laser emitted by the light source is used for intensity modulation with the detected microwave, generation of a local optical comb with a small repetition frequency difference, and detection of the optical comb. The intensity-modulated signal is frequency-mixed with the radio frequency-modulated local optical comb and the radio frequency-modulated detection optical comb, respectively. Based on the vernier effect, the position of the comb tooth close to the microwave frequency to be measured is determined according to the difference between the frequency differences of the two frequency-mixed signals, and the microwave frequency is accurately positioned to the left, right or middle of the comb tooth position of the local optical comb and the detection optical comb, and then the microwave signal frequency is obtained.

[0006] The present invention relates to a system for implementing the above-mentioned method, comprising: a laser, a light splitting module, two dual-drive Mach-Zehnder modulators, an intensity modulator, two coherent receiving modules, and a signal processing module, wherein: the light splitting module splits the laser light generated by the laser into three paths, two of which are respectively input into the first and second dual-drive Mach-Zehnder modulators to generate a flat local optical comb and a detection optical comb; the third path modulates a microwave signal to be measured onto the laser light through the intensity modulator; the first and second coherent receiving modules respectively collect beat frequency signals between the modulated light containing the microwave signal to be measured and the two flat optical combs; the signal processing module performs ADC conversion on the collected signal, and then performs data processing and demodulation using a vernier method to obtain the instantaneous microwave signal frequency to be measured.

[0007] Technical Effects

[0008] The present invention uses two dual-driven Mach-Zehnder modulators to generate two sets of flat optical frequency combs with a small repetition frequency difference, and uses the vernier effect to measure the frequency of the detection microwave frequency modulated on continuous light. It not only has high measurement accuracy and large instantaneous bandwidth, but also can measure multiple microwave frequencies.

[0009] Compared to existing technologies, the present invention is unaffected by phase relationships. Electro-optical modulation is used to generate two optical frequency comb signals with a slight repetition frequency difference. The microwave signal to be measured is loaded onto an intensity modulator, generating a double-sideband (DSB) signal from the single-frequency light. All modulators in the system use the same seed light, resulting in excellent mutual coherence. The two optical comb signals interfere with the microwave-loaded optical signal, respectively, and perform beat frequency measurement. The microwave frequency is then calculated and demodulated using the Vernier effect, enabling accurate and efficient frequency measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the present invention;

[0011] Figure 2 The flat light comb generated for this embodiment;

[0012] Figure 3 This is a schematic diagram of microwave frequency demodulation in this embodiment;

[0013] Figure 4 Schematic diagram of the detection frequency of the optical signal and the dual optical comb in this embodiment;

[0014] In the figure: f0 is the center frequency of the light source, the dashed and dotted lines are the spectral lines of the local optical comb and the detection optical comb with a small repetition frequency difference, and the straight line is the microwave frequency modulated on the continuous light;

[0015] Figure 5 Spectra of the beat frequencies of the single-frequency microwave signal and the dual optical comb in this embodiment;

[0016] Figure 6The frequency spectrum diagram of the multi-frequency microwave signal and the double optical comb respectively;

[0017] In the figure: main laser 1, 70 / 30 fiber coupler 2, first 50 / 50 fiber coupler 3, first double drive Mach-Zehnder modulator 4, first radio frequency signal generator 5, first direct current voltage source 6, second double drive Mach-Zehnder modulator 7, second radio frequency signal generator 8, second direct current voltage source 9, intensity modulator 10, signal source to be measured 11, third direct current voltage source 12, second 50 / 50 fiber coupler 13, third 50 / 50 fiber coupler 14, first photodetector 15, first analog-to-digital converter 16, third 50 / 50 fiber coupler 17, second photodetector 18, second analog-to-digital converter 19, fiber coupler first port~third port a~c. DETAILED DESCRIPTION

[0018] As Figure 1As shown, this embodiment relates to an instantaneous microwave frequency measurement system based on a dual electro-optical comb, comprising: a master laser 1, a 70 / 30 fiber coupler 2, a first 50 / 50 fiber coupler 3, a first dual-drive Mach-Zehnder modulator 4, a first RF signal generator 5, a first DC voltage source 6, a second dual-drive Mach-Zehnder modulator 7, a second RF signal generator 8, a second DC voltage source 9, an intensity modulator 10, a third DC voltage source 12, a second 50 / 50 fiber coupler 13, a third 50 / 50 fiber coupler 14, a first photodetector 15, a first analog-to-digital converter converter 16, a third 50 / 50 fiber coupler 17, a second photodetector 18, and a second analog-to-digital converter 19, wherein: the master laser 1 is connected to the first port a of the 70 / 30 fiber coupler 2, the second port b of the 70 / 30 fiber coupler 2 and the third port c have a splitting ratio of 70:30, the second port b of the 70 / 30 fiber coupler 2 is connected to the first port a of the first 50 / 50 fiber coupler 3, the second port b of the first 50 / 50 fiber coupler 3 is connected in sequence to the first dual-drive Mach-Zehnder modulator 4, the second port b of the third 50 / 50 fiber coupler 14, the first photodetector 18, and the second analog-to-digital converter 19. The detector 15 is connected to the first analog-to-digital converter 16, the first RF signal generator 5 is connected to the first dual-drive Mach-Zehnder modulator 4, the first DC voltage source 6 is connected to the first dual-drive Mach-Zehnder modulator 4, the third port c of the first 50 / 50 fiber coupler 3 is connected in sequence to the second dual-drive Mach-Zehnder modulator 7, the second port b of the fourth 50 / 50 fiber coupler 17, the second photodetector 18, and the second analog-to-digital converter 19, the second RF signal generator 8 is connected to the second dual-drive Mach-Zehnder modulator 7, the second DC voltage source 9 is connected to the first dual-drive Mach-Zehnder modulator The third port c of the 70 / 30 fiber coupler 2 is connected to the intensity modulator 10 and the second 50 / 50 fiber coupler 13 in sequence. The third DC voltage source 12 is connected to the intensity modulator 10. The second port b of the second 50 / 50 fiber coupler 13 is connected to the third port c of the third 50 / 50 fiber coupler 14, the first photodetector 15, and the first analog-to-digital converter 16 in sequence. The third port c of the second 50 / 50 fiber coupler 13 is connected to the third port c of the fourth 50 / 50 fiber coupler 17, the second photodetector 18, and the second analog-to-digital converter 19 in sequence.

[0019] The master laser 1 generates laser light with a wavelength of 1550 nm and a constant power of 10 mW, which is transmitted to a 70 / 30 fiber coupler 2 and split into two paths: one path serves as the input light for the optical comb, and the other serves as the light source for the intensity modulator. The optical comb input light is then split into two paths by a first 50 / 50 fiber coupler 3: one path serves as the input light for the local optical comb, and the other serves as the input light for the detection optical comb. The input light for the local optical comb enters a first dual-drive Mach-Zehnder modulator 4. A first RF signal generator 5 generates an RF signal at the upper limit frequency, which is modulated onto the first dual-drive Mach-Zehnder modulator 4. A first DC voltage source 6, set to 3 V, provides a bias voltage for the first dual-drive Mach-Zehnder modulator 4. The input light for the detection optical comb enters a second dual-drive Mach-Zehnder modulator 7. A second RF signal generator 8 generates an RF signal at the lower limit frequency, which is modulated onto the second dual-drive Mach-Zehnder modulator 7. A second DC voltage source 9, set to 1.4 V, provides a bias voltage for the second dual-drive Mach-Zehnder modulator 7. By changing the phase of the upper and lower RF signals of the first dual-drive Mach-Zehnder modulator 4 and the second dual-drive Mach-Zehnder modulator 7, a flat optical comb is generated when the phase difference and the amplitude difference satisfy ΔA±Δθ=π, where the phase difference Amplitude difference V1 and V2 are the RF signal amplitudes applied to the upper and lower arms of the dual-drive Mach-Zehnder modulator, respectively. π is the half-wave voltage of the dual-drive Mach-Zehnder modulator, V b is the bias voltage applied. The input light of the intensity modulator enters the intensity modulator 10 through the input port. The third DC voltage source 12 applies a bias voltage of 4V to the intensity modulator so that the intensity modulator operates in the linear modulation area. In this embodiment, a microwave signal with a frequency of the upper limit frequency is generated by the arbitrary signal generator 11 as a detection signal and modulated onto the intensity modulator 10. At this time, the detection signal is modulated onto the optical carrier and divided into two paths through the second 50 / 50 fiber coupler 13, one path beats with the local optical comb and the other path beats with the detection optical comb. The beat result is photoelectrically detected by the first photodetector 15 and the second photodetector 18 respectively, and the detected signal is respectively collected and processed by the first analog-to-digital converter 16 and the second analog-to-digital converter 19.

[0020] In this embodiment, the upper limit frequency and the lower limit frequency are set to 5 GHz and 4.99 GHz respectively.

[0021] like Figure 4 As shown, the signal acquisition and data processing are specifically as follows: the detection optical signal beats with the local optical comb and the detection optical comb respectively, and the difference between the two beat frequencies is Δf1-Δf2=nΔf r =nf r1 -nf r2, where: Δf1 and Δf2 are the beat frequency differences between the detection signal and the local optical comb and the detection optical comb, respectively, f r1 and f r2 are the repetition frequencies of the two optical combs, Δf r is the repetition frequency difference of the dual optical comb.

[0022] When the microwave frequency modulated on the continuous light is on the right side of the nth comb tooth, the frequency of the detected microwave signal is f RF =nf r2 +Δf2=nf r1 +Δf1; when the microwave frequency modulated on the continuous light is to the left of the nth comb tooth, the detected microwave signal frequency is f RF =nf r2 -Δf2=nf r1 -Δf1; when the microwave frequency modulated on the continuous light is in the middle of the nth comb tooth, the frequency of the detected microwave signal is f RF =nf r2 +Δf2=nf r1 -Δf1.

[0023] Since the detection optical signal and the two optical combs originate from the same light source, center frequency drift of the light source need not be considered in this embodiment; the effects of frequency drift can be eliminated after the beat frequency is applied. The system calibrates the RF signal generator modulating the dual-drive Mach-Zehnder modulator, the signal source under test, the oscilloscope, and the rubidium atomic clock.

[0024] Preferably, the microwave signal is a multi-frequency microwave signal. Assuming the number of input microwave signals is n, after passing through the intensity modulator, it is subjected to a beat frequency reaction with the dual optical comb. This beat frequency reaction results in n spectral lines in the local optical comb and the detection optical comb, respectively. The multi-frequency signal can then be demodulated using the frequency measurement scheme described above.

[0025] like Figure 3 As shown, the two optical combs of the present invention serve as reference paths for each other, and the detection microwave signal is modulated onto continuous light through an intensity modulator, and then beats with the two optical combs respectively.

[0026] After specific practical experiments, the frequency measurement experiment of 5.1GHz single-frequency microwave signal was carried out and the results were obtained. Figure 5 The frequency spectrum of the single-frequency microwave signal and the dual optical comb is shown. As shown in the figure, the beat frequency of the local optical comb and the detection microwave signal is 100MHz, and the beat frequency of the detection optical comb and the detection microwave signal is 110MHz. According to the formula Δf1-Δf2=nΔf r =nf r1 -nf r2, that is, n is 1, that is, the frequency of the detected microwave signal is located near the first tooth of the optical comb, and because the detection optical comb beat frequency result is greater than the local optical comb beat frequency result, the frequency spectrum of the detected microwave signal is located to the right of the first tooth of the local optical comb, and the frequency difference is 100MHz. Similarly, the frequency spectrum of the detected microwave signal is located to the right of the first tooth of the detection optical comb, and the frequency difference is 100MHz, that is, f RF =f r2 +Δf2=f r1 +Δf1. The final detection signal frequency is 5.1 GHz.

[0027] This embodiment further conducts frequency measurement experiments on multi-frequency microwave signals consisting of 0.3 GHz, 5.2 GHz, 10.4 GHz, and 15.1 GHz, and obtains Figure 6 The frequency spectrum of the multi-frequency microwave signal and the dual optical comb is shown. As shown in the figure, the beat frequencies of the local optical comb and the detection microwave signal are located at 100MHz, 200MHz, 300MHz and 400MHz respectively, and the beat frequencies of the detection optical comb and the detection microwave signal are located at 130MHz, 210MHz, 300MHz and 420MHz respectively. According to the frequency measurement formula Δf1-Δf2=nΔf r =nf r1 -nf r2 , that is, the four spectral lines corresponding to n are 3, 1, 0 and 2, which correspond to the third optical comb, the first optical comb, the central optical comb and the second optical comb respectively. And according to the comparison of the detection signal with the detection optical comb and the local optical comb beat frequency results, it can be concluded that the spectral lines corresponding to the detected multi-frequency signal are all located on the right side of the corresponding spectral line. According to the formula f RF =f r2 +Δf2=f r1 +Δf1, and finally the corresponding frequencies of the detected multi-frequency signal are 0.3GHz, 5.2GHz, 10.2GHz and 15.1GHz. The present invention achieves an instantaneous measurement bandwidth of 0-40GHz, a frequency accuracy of less than or equal to 5MHz, and a processing delay of less than or equal to 200ns.

[0028] Compared with existing technologies, the present invention utilizes dual optical combs to measure microwave frequencies, leveraging the advantages of wavelength division multiplexing (WDM). The coherent interference of the dual optical combs is detected by a photodetector, allowing a single detector to simultaneously demodulate all frequency components, eliminating the need for complex dispersion and WDM processes. Furthermore, as the number of channels in a WDM scheme increases, the number of receiving devices also increases, leading to increased system complexity and cost. Furthermore, the present invention directly modulates the microwave frequency to be measured on an intensity modulator, allowing the amplitude spectrum to intuitively identify the presence of new components, eliminating the need for phase modulation and subsequent demodulation of each component. This demonstrates that the present invention also reduces back-end demodulation complexity.

[0029] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principles and purpose of the present invention. The scope of protection of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. All implementation schemes within its scope shall be subject to the constraints of the present invention.

Claims

1. A method for measuring instantaneous microwave frequency based on a dual electro-optical comb, characterized in that: The laser light emitted by the light source is used to perform intensity modulation with the detection microwave, generate a local optical comb, and generate a detection optical comb. The intensity modulated signal is then beat with the local optical comb modulated by RF and the detection optical comb modulated by RF. Based on the vernier effect, the position of the comb teeth close to the microwave frequency to be measured is determined according to the difference between the two beat frequencies, and the microwave frequency is accurately located to the left, right, or middle of the local optical comb and the detection optical comb teeth, thereby obtaining the microwave signal frequency.

2. The instantaneous microwave frequency measurement method based on dual electro-optical comb according to claim 1 is characterized in that: The difference between the two beat frequencies is Δf1-Δf2=nΔf r =nf r1 -nf r2 , where: Δf1 and Δf2 are the beat frequency differences between the detection signal and the local optical comb and the detection optical comb, respectively, f r1 and f r2 are the repetition frequencies of the two optical combs, Δf r is the repetition frequency difference of the dual comb; When the microwave frequency modulated on the continuous light is on the right side of the nth comb tooth, the frequency of the detected microwave signal is f RF =nf r2 +Δf2=nf r1 +Δf1; when the microwave frequency modulated on the continuous light is to the left of the nth comb tooth, the detected microwave signal frequency is f RF =nf r2 -Δf2=nf r1 -Δf1; when the microwave frequency modulated on the continuous light is in the middle of the nth comb tooth, the frequency of the detected microwave signal is f RF =nf r2 +Δf2=nf r1 -Δf1.

3. A system for implementing the instantaneous microwave frequency measurement method based on dual electro-optical combs according to claim 1 or 2, characterized in that: include: The invention relates to a laser, a light splitting module, two dual-driven Mach-Zehnder modulators, an intensity modulator, two coherent receiving modules and a signal processing module, wherein the light splitting module splits the laser light generated by the laser into three paths, two of which are respectively input into the first and second dual-driven Mach-Zehnder modulators to generate a flat local optical comb and a detection optical comb, the third path modulates the microwave signal to be measured onto the laser through the intensity modulator, the first and second coherent receiving modules respectively collect the beat frequency signals of the modulated light containing the microwave signal to be measured and the two flat optical combs, and the signal processing module performs ADC conversion on the collected signal and then performs data processing and demodulation through the vernier method to obtain the instantaneous microwave signal frequency to be measured.

4. The system according to claim 3, wherein: Specifically comprising: a master laser, a 70 / 30 fiber coupler, a first 50 / 50 fiber coupler, a first dual-driven Mach-Zehnder modulator, a first RF signal generator, a first DC voltage source, a second dual-driven Mach-Zehnder modulator, a second RF signal generator, a second DC voltage source, an intensity modulator, a third DC voltage source, a second 50 / 50 fiber coupler, a third 50 / 50 fiber coupler, a first photodetector, a first analog-to-digital converter, a third 50 / 50 fiber coupler, a second photodetector, and a second analog-to-digital converter, wherein: the master laser is connected to the first port of the 70 / 30 fiber coupler, the second port and the third port of the 70 / 30 fiber coupler have a splitting ratio of 70:30, the second port of the 70 / 30 fiber coupler is connected to the first port of the first 50 / 50 fiber coupler, the second port of the first 50 / 50 fiber coupler is connected to the first dual-driven Mach-Zehnder modulator, the second port of the third 50 / 50 fiber coupler, the first photodetector, the first analog-to-digital converter, and the third 50 / 50 fiber coupler. The invention relates to a fiber optic coupler comprising a first 50 / 50 optical fiber coupler and a second 50 / 50 optical fiber coupler. The first 50 / 50 optical fiber coupler is connected to a first dual-drive Mach-Zehnder modulator, a first DC voltage source is connected to the first dual-drive Mach-Zehnder modulator, a third port of the first 50 / 50 optical fiber coupler is connected to the second dual-drive Mach-Zehnder modulator, a second port of the fourth 50 / 50 optical fiber coupler, a second photodetector, and a second analog-to-digital converter in sequence, a second RF signal generator is connected to the second dual-drive Mach-Zehnder modulator, a second DC voltage source is connected to the first dual-drive Mach-Zehnder modulator, a third port of the 70 / 30 optical fiber coupler is connected to the intensity modulator and the second 50 / 50 optical fiber coupler in sequence, a third DC voltage source is connected to the intensity modulator, the second port of the second 50 / 50 optical fiber coupler is connected to the third port of the third 50 / 50 optical fiber coupler, the first photodetector, and the first analog-to-digital converter in sequence, and the third port of the second 50 / 50 optical fiber coupler is connected to the third port of the fourth 50 / 50 optical fiber coupler, the second photodetector, and the second analog-to-digital converter in sequence.

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